This invention relates generally to "flowing arch" expansion joints and more particularly to an improved layered construction for such joints. The nature and background of "flowing arch" expansion joints, also known as "shallow arch" joints, are thoroughly described in prior U.S. Pat. No. 4,241,944 which is assigned, also, to the assignee of the present invention.
As described in the cited prior patent, the text of which is considered to be incorporated by reference into this application, resilient expansion joints generally take one of two principal forms. The shallow or flowing arch, is one form, and the other is known variously as a narrow arch or abrupt arch, but these other types of expansion joints form no part of this invention.
In the past, flowing arch joints have been fabricated using built-up winding techniques and/or related molding processes, for the purpose of achieving the desired "bulged cylinder" shape in the conduit that forms the central part of such a joint. It has been explained in the cited prior art patent, among others, that flexibility and pressure-resistant strength are two important structural requirements of flowing arch expansion joints.
The shape of so-called narrow arch joints tends to lead naturally to certain physical characteristics, such as desirable radial strength, that are not present to an equivalent extent in the flowing arch shape. As a result, materials and techniques used acceptably in the construction of narrow arch joints in the past, have been considered unacceptable and/or undesirable for use in flowing arch joints. Specifically, narrow-arch joints known in the prior art, such as catalog items 200 and 200HP, manufactured and sold by the Assignee of the present invention, have incorporated an inner "liner" layer of fluoropolymer material such as FEP (fluorinated ethylene propylene), surrounded by a layer of fiberglass fabric material which is in turn surrounded by one layer of elastomeric material and reinforced with a plurality of fabric plies and steel rings and further covered with an outer layer of elastomeric material. In this prior art construction, heating of the layered materials in a confining jacket, has been used to cause the inner layer of FEP material and the surrounding layer of elastomeric material to mechanically bond to the interposed fiberglass fabric layer.
Am expansion joint construction having fiberglass fabric in contact with the FEP liner and extending from one end of the expansion joint to the other, has not been used previously in the manufacture of flowing arch expansion joints because it was believed that the fabric material would not accommodate the range of flexibility required; it was believed also, that such a construction could not be made to withstand the pressure forces generated when pressurized fluids are contained within the passage through the expansion joint. Tests have demonstrated that fiberglass-layer construction, of the type previously used in narrow arch joints, often results in separation of the fiberglass fabric seam and subsequent failure of the joint when used in flowing arch construction, without benefit of this invention.